The present invention relates to a drill bit having saddles for a number of roller cutters, said cutters having rows of cutting means, e.g., hard material inserts, extending along the circumference of the roller cutter, said rows being displaced in the axial direction of the roller cutter. A saddle and the adherent roller cutter are so designed that the roller cutter is reversibly mountable in the saddle. The invention also relates to a roller cutter to be used in said drill bit.
When drilling with such a drill bit the hardness of the rock varies between different drill holes. An aim of the present invention is to optimize the drilling in order to achieve the highest possible penetration rate regardless of the hardness of the rock formation. This means that in softer rock formations a bigger distance between the rows should be used than in harder rock formations. At the same time, the invention intends to make it possible to optimize the drilling without having to change the type of roller cutters of the drill bit.
From Swedish Application 7900922-1 a drill bit is previously known. In said drill bit the distance between the rows of the cutting means can be varied by exchange of a roller cutter of a first collection for a roller cutter of a second collection. This known drill bit arrangement however requires two collections of roller cutters while the present invention intends to make it possible to vary the distance between rows by one single type of roller cutter. From German Patent 1805336 a drill bit is previously known, said drill bit makes it possible to vary the distance between rows by removing a supporting arm carrying a number of roller cutters and thus also removing said roller cutters. In this known drill bit the roller cutters are not selectively exchangeable for one another.